High-energy bremsstrahlung emission can occur owing to electron scattering in the nuclei or ions Coulomb field following the relativistic-electron generation in high-intensity laser interaction with plasmas. Such emission of photons in the keV-MeV energy range is of interest to characterize the relativistic electron populations and develop laser-based photons sources. Even if it is a well-established and widely studied emission process, its modeling in laser-plasma scenarios needs further investigation. Moreover, advanced near-critical double-layer targets (DLTs), consisting in a low-density foam deposited on a thin solid substrate, have never been explored extensively for bremsstrahlung photon emission. Therefore, in this paper, we show the rationale, advantages, limitations, application regime, and complementarity of different modeling approaches and apply them to the unconventional configuration based on DLTs. We couple multi-dimensional particle-in-cell simulations with a Monte Carlo strategy to simulate bremsstrahlung in two ways: integrated into the particle-in-cell loop itself or after the simulation with two separate codes. We also use simplified semi-analytical relations to retrieve the photon properties starting only from information on the relativistic electrons. With these tools, we investigate bremsstrahlung emission when an ultra-intense laser (0.8 μm wavelength, 30 fs duration, a0=20 and 3 μm waist) interacts with DLTs having different properties. Despite some limitations of the numerical tools, we find that all approaches significantly agree on the characteristics of ∽1-100 MeV photon emission. This points to the possibility of adopting the different modeling approaches in a complementary way while at the same time identifying the best suited for a specific scenario. Regardless, DLTs appear to overall boost the high energy photon emission while at the same time enabling control of the emission itself.

Non-destructive material characterization exploiting radiation sources is of crucial importance in several fields ranging from the characterization of artworks to environmental monitoring. For instance, Ion Beam Analysis techniques exploiting particle accelerators stand for their unparalleled detection capabilities. However, the wide use of these techniques is limited by the large costs and dimensions of the exploited sources. In this framework, laser-driven particle acceleration represents a promising alternative to conventional sources since it can address some of their limitations. It relies on the interaction of a super-intense ultrashort laser pulse with a target material to accelerate high-energy electrons and ion bunches. Laser-driven radiation sources are potentially more compact and cheaper than particle accelerators. Moreover, the same laser source can provide different radiations by acting on the target configuration. Besides electrons and ions, high-energy photons and neutrons can be produced by exploiting suitable converter materials. Lastly, the particle energies can be controlled by tuning both the laser intensity and target properties. Here, we show some of the most recent results related to the application of laser-driven radiation sources to materials characterization. Our strategy is based on advanced near-critical Double-Layer Targets (DLT) to enhance the acceleration process. By means of experimental and numerical tools, we show how laser-driven protons, electrons, photons, and neutrons can be exploited for surface and bulk elemental analysis, as well as radiography. Notably, DLTs allow for satisfying the requirements of the techniques, in terms of energies and fluxes, with reduced laser requirements.

Non-linear inverse Compton scattering (NICS) is of significance in laser-plasma physics and for application-relevant laser-driven photon sources. Given this interest, we investigated this synchrotron-like photon emission in a promising configuration achieved when an ultra-intense laser pulse interacts with a double-layer target (DLT). Numerical simulations with two-dimensional particle-in-cell codes and analytical estimates are used for this purpose. The properties of NICS are shown to be governed by the processes characterizing laser interaction with the near-critical and solid layers composing the DLT. In particular, electron acceleration, laser focusing in the low-density layer, and pulse reflection on the solid layer determine the radiated power, the emitted spectrum, and the angular properties of emitted photons. Analytical estimates, supported by simulations, show that quantum effects are relevant at laser intensities as small as ∼1021 W/cm2 Target and laser parameters affect the NICS competition with bremsstrahlung and the conversion efficiency and average energy of emitted photons. Therefore, DLT properties could be exploited to tune and enhance photon emission in experiments and future applications.